1. Field of the Invention
The present invention relates generally to storage tank safety pressure relief methods and systems, and more particularly, to methods and systems for preventing overpressure conditions in storage tanks containing pressurized volatile liquids whereby vapors vented from the storage tanks are prevented from entering the atmosphere.
2. Background of the Invention
Pressurized volatile liquids such as nitrogen, hydrogen, ammonia, carbon dioxide and hydrocarbons, e.g., ethylene and liquified petroleum gases (LPG), are commonly transported or stored in tank cars, tank trailers and other storage tanks. For example, in areas where natural gas is unavailable, LPG is often utilized for the heating of homes and places of business, and each home or place of business includes one or more permanent LPG storage tanks located nearby. LPG storage tanks are also mounted on vehicles, such as pickup trucks, for supplying fuel to the engines thereof which have been converted for propane use. The term "storage tank" is used hereinafter to mean any closed container or tank utilized for containing a pressurized volatile liquid.
Most, if not all, storage tanks for containing volatile liquid are equipped with conventional pressure relief valves for preventing overpressure. That is, if a predetermined pressure level is reached within the storage tanks, the pressure relief valves communicated therewith open whereby vapors are vented to the atmosphere. While such venting of vapors to the atmosphere relieves pressure from the storage tanks and prevents dangerous overpressure, it often produces the adverse result of polluting the atmosphere and creating fire and explosion hazards. For example, if an LPG storage tank is over-filled with LPG and allowed to be heated by the sun or otherwise, a pressure level can quickly be reached within the storage tank which causes the pressure relief valve connected thereto to open and LPG vapors to be vented to the atmosphere. Numerous fires and explosions have occurred as a result of such vented LPG vapors being accidentally ignited. Thus, there is a need for a volatile liquid storage tank safety pressure relief method and system whereby when pressure is relieved from a storage tank by the venting of vapors therefrom due to over-filling, heating, etc., the vented vapors are prevented from entering the atmosphere.